The availability of healthy, well-defined animals is critical to biomedical research. There currently exists a special need for nonhuman primates free of simian retroviruses for use in AIDS-related research. Availability of these animals for development and evaluation of drugs and vaccines for treatment and prevention of AIDS is a critical world-wide need. This proposal requests continued funding to maintain and expand the existing specific pathogen-free (SPF) breeding colonies of rhesus monkeys (Macaca mulatta) and pigtail monkeys (Macaca nemestrina). The existing breeding colonies of 250 adult and juvenile M. mulatta and 100 adult and juvenile M. nemestrina would be expanded to a population of 584 adult and juvenile M. mulatta and 157 M. nemestrina by retaining the majority of the female offspring and sufficient male offspring to establish additional harem breeding groups in expanded outdoor holding facilities. The established programs for routine health monitoring and testing to assure the colonies are free of the target pathogens (Herpesvirus simiae, SIV, STLV-l and SRV) would be continued. Surplus male and female offspring would be made available to the biomedical research community for AIDS- related research. Establishment of a small program for production of timed-pregnant female SPF macaques is also proposed to make this unique animal model available for research on the emerging crisis of pediatric AIDS.